Tumors use tryptophan-catabolizing enzymes such as indoleamine 2,3-dioxygenase (IDO-1) to induce an immunosuppressive environment. IDO-1 is induced in response to inflammatory stimuli and promotes immune tolerance through effector T-cell anergy and enhanced Treg function. As such, IDO-1 is a nexus for the induction of a key immunosuppressive mechanism and represents an important immunotherapeutic target in oncology. Starting from HTS hit 5, IDO-1 inhibitor 6 (EOS200271/PF-06840003) has been developed. The structure-activity relationship around 6 is described and rationalized using the X-ray crystal structure of 6 bound to human IDO-1, which shows that 6, differently from most of the IDO-1 inhibitors described so far, does not bind to the heme iron atom and has a novel binding mode. Clinical candidate 6 shows good potency in an IDO-1 human whole blood assay and also shows a very favorable ADME profile leading to favorable predicted human pharmacokinetic properties, including a predicted half-life of 16-19 h.

Metastatic melanoma is the most aggressive skin cancer. Recently, phenotypically distinct subpopulations of tumor cells were identified. Among them, ABCB5-expressing cells were proposed to display an enhanced tumorigenicity with stem cell-like properties. In addition, ABCB5+ cells are thought to participate to chemoresistance through a potential efflux function of ABCB5. Nevertheless, the fate of these cells upon drugs that are used in melanoma chemotherapy remains to be clarified. Here we explored the effect of anti-melanoma treatments on the ABCB5-expressing cells. Using a melanoma xenograft model (WM266-4), we observed in vivo that ABCB5-expressing cells are enriched after a temozolomide treatment that induces a significant tumor regression. These results were further confirmed in a preliminary study conducted on clinical samples from patients that received dacarbazine. In vitro, we showed that ABCB5-expressing cells selectively survive when exposed to dacarbazine, the reference treatment of metastatic melanoma, but also to vemurafenib, a new inhibitor of the mutated kinase V600E BRAF and other various chemotherapeutic drugs. Our results show that anti-melanoma chemotherapy might participate to the chemoresistance acquisition by selecting tumor cell subpopulations expressing ABCB5. This is of particular importance in understanding the relapses observed after anti-melanoma treatments and reinforces the interest of ABCB5 and ABCB5-expressing cells as potential therapeutic targets in melanoma.

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Tumors use indoleamine 2,3-dioxygenase-1 (IDO1) as a major mechanism to induce an immunosuppressive microenvironment. IDO1 expression is upregulated in many cancers and considered to be a resistance mechanism to immune checkpoint therapies. IDO1 is induced in response to inflammatory stimuli such as IFNg and promotes immune tolerance by depleting tryptophan and producing tryptophan catabolites, including kynurenine, in the tumor microenvironment. This leads to effector T-cell anergy and enhanced T reg function through upregulation of FoxP3. As a nexus for the induction of key immunosuppressive mechanisms, IDO1 represents an important immunotherapeutic target in oncology. Here, we report the identification and characterization of the novel selective, orally bioavailable IDO1 inhibitor EOS200271/PF-06840003. It reversed IDO1-induced T-cell anergy in vitro. In mice carrying syngeneic tumor grafts, PF-06840003 reduced intratumoral kynurenine levels by over 80% and inhibited tumor growth both in monotherapy and, with an increased efficacy, in combination with antibodies blocking the immune checkpoint ligand PD-L1. We demonstrate that anti-PD-L1 therapy results in increased IDO1 metabolic activity thereby providing additional mechanistic rationale for combining PD-(L)1 blockade with IDO1 inhibition in cancer immunotherapies. Supported by these preclinical data and favorable predicted human pharmacokinetic properties of PF-06840003, a phase I open-label, multicenter clinical study (NCT02764151) has been initiated.

Cold static preservation on ice (~4°C) remains the clinical standard of donor organ preservation. However, mitochondrial injury develops during prolonged storage, which limits the extent of time that organs can maintain viability. We explored the feasibility of prolonged donor lung storage at 10°C using a large animal model and investigated mechanisms related to mitochondrial protection. Functional assessments performed during ex vivo lung perfusion demonstrated that porcine lungs stored for 36 hours at 10°C had lower airway pressures, higher lung compliances, and better oxygenation capabilities, indicative of better pulmonary physiology, as compared to lungs stored conventionally at 4°C. Mitochondrial protective metabolites including itaconate, glutamine, and N-acetylglutamine were present in greater intensities in lungs stored at 10°C than at 4°C. Analysis of mitochondrial injury markers further confirmed that 10°C storage resulted in greater protection of mitochondrial health. We applied this strategy clinically to prolong preservation of human donor lungs beyond the currently accepted clinical preservation limit of about 6 to 8 hours. Five patients received donor lung transplants after a median preservation time of 10.4 hours (9.92 to 14.8 hours) for the first implanted lung and 12.1 hours (10.9 to 16.5 hours) for the second. All have survived the first 30 days after transplantation. There was no grade 3 primary graft dysfunction at 72 hours after transplantation, and median post-transplant mechanical ventilation time was 1.73 days (0.24 to 6.71 days). Preservation at 10°C could become the standard of care for prolonged pulmonary preservation, providing benefits to both patients and health care teams.